Hopefully I can get the 21-CT-55 up and running soon, then I will have a pic with a modern monitor, 21CYP22, 21AXP22A (grey), 21AXP22 (green), and green face 21FBP22.

My CTC-136B is wide-band, manufactured in 1986, and has the I-Q chipset. I'll look at the SAMS to see about the single-ended I delay line. I'm getting much from the topic of the "glow" that may be due to grid contamination. I'll see if I can find an hour or more later tonight to fire up my 4, and look for the glow. Thanks for all the info!
Kevin

21FBP22A Reds vs Sonys
 

I have now performed the above Photo Impact “spectrum analysis” on some of my 21CT55 screenshots verses ’84 Sony pro monitor and ’97 Sony 27in tv. All pics were shot with the same Canon S40 and were not color enhanced. I used the DVE color bar for all screenshots tests and “normalized” each pic by placing the virtual sampling probe onto each white bar and setting the brightness to produce approximately the same digital 255 max red, green and blue components. I then placed the sampling probe onto the red bar and took digital readings of its red, green and blue components. Ideally, a perfectly pure red bar should produce a red component of 255 while its green and blue components should read zero. Only the color accuracy of the Canon camera sensor is evolved here since the LCD computer monitor’s color accuracy is never an issue. Since relative CRT phosphor chroma response is all we are interested in, any variance of these readings indicates contamination of the ideal red phosphor’s light output, right?

Preliminary estimates of red phosphor purity of a ’88 13in Sony pro monitor, a ’97 27in Sony "modern" tv and of course the 21CT55 with 21FBP22A “rare-earth” crt follows:

21in FBA.……………Red contaminated with 5.6% green and 8.2% blue
13in Sony……………Red contaminated with 12.6% green and 6.3% blue
27in Sony……………Red contaminated with 29.2% green and 21.3% blue

No wonder the “modern” TV crts appear orangish red!

Those numbers for the 27 inch Sony should correspond to a visually washed out red - something is not right with those numbers, unless you report that visually it appears that bad.

In regards to "the red bar color should normalize to (255,0,0) RGB," I'm afraid it just ain't so, for a whole slew of reasons: the impossibility of getting ideal filters in the camera, the different spectra of the displays that interact with the filters in the camera; the raw to jpg conversion in the camera having a matrix that is designed to give pleasing color, not accurate color; deliberate non-linear S-curve processing in the camera to mimic the pleasing contrast response of film; etc. etc. etc. etc.

The human eye is a much better instrument for these comparisons than a digital camera.

21FBP22A vs 15GP22/21AXP22
 

Wayne, thanks for the reply. I reran the 27in Sony by brightening the white bar. It was way too dark before which caused the red bar to saturate and as you said, "wash-out". The new results:
21in FBA.……………Red contaminated with 5.6% green and 8.2% blue
13in Sony……………Red contaminated with 12.6% green and 6.3% blue
27in Sony……………Red contaminated with 29.2% green and 21.3% blue

Somewhat less contaminated but still way orangish red compared to the Sony pro and the 21CT55 with 21FBP22A. The stated 255,0,0 RGB was "ideal" with no hardware limitations. I believe this simple and cheap method of relative phosphor comparisons can be quite useful when comparing the original NTSC rated crts eg 15GP22 and 21AXP22 with the gray screen 21FBP22A. All I need is optimally setup color bar screenshots of the original GP/AXPs. I don't have much hope for a live eyeball shootout that includes the gray screen 21FBP22A, certainly not one I may witness.

Wouldn't the kelvin temp of the LCD monitor backlights be an issue, or is that somehow compensated for/already calibrated/or not an issue?

Mind you, I'm a amateur with all of this, but my two LCD monitors have two Kelvin settings that affect the color spectra - 6500K (default) and 9300K.

Interesting thread! I've worked TV's for 30+ years and about all the discussion I've ever heard is from a old, now-dead TV tech that swore by the "old" RCA red versus the "new" RCA red. I guess he too would've been interested in this thread.

I'm learning, keep posting!

Cheers,

Tom-

That is a very interesting test. Are you able to set the camera into a completely "manual" mode, so it doesn't do any type of color balancing on its own? If so, do you also need to pick a starting color-balance mode? I know mine has several settings for modes but I have not studied its operation very much.

This is still a little suspicious. Getting purer colors when the drive is turned up could indicate that the black level is a little high or there are reflections of room light. This would be a valid test of how the tube is set up and viewed, but not necessarily the characteristics of the red phosphor color alone. To get the comparison of the pure phosphor colors you need to do two things:
1) take the picture in a completely dark room, making sure there are no reflections (like from your shirt)
2) turn up the color control and adjust the tint if necessary to make sure only the red beam is on and the other two beams are completely cut off.
2b) Since the color demodulator may include color corrections that deliberately make the primary bars impure, you may need to readjust the tint individually for each primary color if you want to measure the green and blue also.

Why not use one of the TV tools with 'gun killers'? They include a feature which shunts the guns grids through a 100k resistor at the flip of a switch, though you could do it with clips as well.

Phosphor Purity Analysis
 

Some misconceptions regarding this phosphor spectral analysis procedure seems to exist. My objective was to evaluate its potential to determine the relative spectral purity of the original NTSC spec’d dim CRTs versus the later, brighter CRTs e.g. 21FBP22A:
1) Only previous informal archive screenshot JPGs were used. No rigorous colorbar setup was used regarding black level, chroma level or luminance (contrast) level. All screenshots were taken in total darkness. Purity and focus were always good.
2) The playback LCD monitor is used only to direct the location of the virtual pointer over the JPG image. It’s chroma characteristics contributes nothing to the JPG phosphor contamination determination. Only the Canon S40 sensor can influence the results.
What is needed now is member postings to this thread their quality colorbar screenshots of their 15GP22, 21CYP22, gray 21AXP22A , green 21AXP22 , green 21FBP22 and gray 21FBP22A all taken in total darkness. Thanks for your interest and cooperation

Just poking around and saw this thread. I was designing televisions at RCA in Indianapolis when the CTC-136 was made. While the Sanyo IC has I/Q demodulation it did not have the wide I channel that was only used in the CTC-131 and CTC-132. I seem to remember the short lived CTC-133 used the same RCA designed chip but the wide I feature was not incorporated. The CTC-121 was the first 25" in the space of a 19" but did not have the Wide I processing..

In those days RCA designed all the IC's in their receivers. I designed the deflection processor in the CTC-146. RCA in Sommerville was the first source and Hitachi was the second source. I remember having to tweak some resistors in the 32 h input circuit as hitachi's transistors behaved a little
different than RCA's.

The CTC-131 chip set included a wide I demodulator and a kine drive IC with auto kine bias. Those were the days....

The CTC-135/136 was a low end chassis designed by RCA Taiwan and overseen by Indianapolis. It used a Sanyo chip that was modified to meet RCA's specs.

I wish i could remember why the Wide I was removed from the CTC-133. Seems there was some reason.. I may have some of those IC's around if I can find them!

JBL-1, my previous post stated that I had a CTC-136B, but it's a 133B. There's a 135 in my daughter's bedroom, and it's not bad for a little Taiwan TV.:yes:
I wasn't aware that the I wasn't wide-band in the 133. The color resolution on my set is really good when compared to the narrow band TV's in the house, and it will reproduce small detail in color, oranges and cyans, etc, but a really good picture. Interesting information, and I thank you for it. I'll look for more info on this and similar chassis where ever I can find it.
Kevin

JBL_1, it's great to hear from someone involved with those sets.

The wideband IC demods were discussed in at least a couple a couple of threads here:

http://www.videokarma.org/showthread...ideband&page=2
See post #19 where I gave a quick explanation the single ended delay line, which, IMO, is one of the cleverest inventions in analog video IC design I have ever seen.

http://www.videokarma.org/showthread...nd#post2434742
See post #132, where I talked about my analysis of a sample RCA set with the wideband circuit while I was working at Zenith. Basically, it looked like the IF couldn't support the increased bandwidth without quadrature distortion, and the high-frequency I gain seemed to be turned down to prevent visible edge effects.

21CT55 Modification Progress Report 1
 

Hi Members...........I have returned back to my 21TC55 "lab test bed" after about six months of doing other techi stuff. When I turned it on
about two weeks ago it came right up but was totally out focus due to CRT blooming. I checked all the standard operational readings I use
for setup: Room Temp=60deg, AC input=115vac, B++=424V, FBI=200ma, boost=770V, ultor=30KV, focus=5.4kv, all normal for this
"experimental" setup. After one hour running, RT was 70deg, AC=115, B++=415V, FBI=199ma, boost=800V, ultor=32KV, focus=5.8KV.
No CRT blooming, fine picture. I measured the CRT heater voltage direct at socket with a true RMS Fluke DMM. It read 6.16vac. I installed
an old CRT booster that raised the heater to 7.64vac. The neck was much brighter of course, so I left the TV on for only a couple of hours.
The set was running at 2% under spec heater all these years and now it was running 20% over spec for two hours. I turned the set off.

Nest morning at 7am, RT was 54. I powered up with booster off, the 21CT55 came up with no bloom in perfect focus! Readings were AC, 115V, B++, 420V, FBI, 200ma, boost, 860v, ultor, 33KV, focus, 5.6KV, heater read 6.01vac. After about 4 hours running with fans off, RT, 74deg, Ac, 115vac, B++, 422, FBI, 190ma, boost, 780v, ultor adjusted to 30KV, focus, 5.7KV, heater, 5.93vac. No blooming, good picture so I measured the FBX temp with digital thermo meter applied direct to primary and EHV secondary. Max temp was 112deg, barely warm!

Pleasant surprise, the CRT shutoff uniform glow problem was greatly reduced, almost unnoticeable! Could it be the 21FBP22 running low heater all these years allowed contamination to build-up on the cathodes causing loss of emission and/or causing grid emission that produced the glow? In-the-day the CRT boosters were quite poplar for restoring brightness and were left in place running at close to 8vac which shortened CRT life considerably. I always took them off after a few days/weeks, often with no noticeable decrease in brightness or increase in blooming.

I still have this problem with the hybrid combination of original CTC2B horizontal oscillator and 6CB5 HOT driving a CTC16 flyback xformer and
associated components, driving the original CTC2B yoke. This mismatch works fine but since it has no width control and only limited centering control, the screen is over scanned about 2 inches and is off center about 1 inch. This is unnoticeable except on test patterns.The BIG problem is the very noticeable horizontal video "fold-over" on the left screen presumably due to the horizontal sweep flyback starting up before the previous field's
video is blanked? The magnetic horizontal deflection of color CRTs is probably the most heavily engineered, most critical component matching
requirement, highest efficiency consumer electronic system of the 1950s. It obviously does not permit the "hacker" approach to customizing I usually pursue. I've tried all the usual modifications using all combinations of resistance, capacitance and inductance to reduce the horizontal width
and enable horizontal centering with no success and almost tragic results. Soooo, I am now designing a video blanking circuit that cuts off the foldover contaminated video for the first portion of every video line. It starts immediately after the chroma burst and extends three microseconds which
completely removes all visible traces of video foldover from the screen. Once I get this circuitry installed into the CTC2B under-chassis I will do a painful optimal convergence and be ready to take a batch of screen shots with Judy's new Sony DSC-HX9V 16.2 mega pixel pocket camera.

The CTC2B with "gray screen" 21FBP22A CRT combination has an extreme dynamic range that displays to the human eye details into deep shadows that our other cameras failed to capture. Hopefully, the Sony camera has a greater low-light dynamic range?

The video gate module is now installed, works perfectly! I'll probably do a convergence tomorrow and if I survive I'll take some screen shots with the Sony..........Tom

Sounds like your CRT is going soft. A strong tube will not lose emission, even at 5.5 volts on the heaters.

I have seen this phenomenon on black and white and color tubes over the years. I suspect the tube is going a bit gassy and the cathodes do contaminate. The higher temperature cleans off the cathodes. That's my guess.

I suspect that over time the emission will diminish somewhat and you will have to burn the cathodes again.

Thanks for the update! Always looking for your posts on the test bed, as they really help others, even those who don't have a CTC-2B.
Going to start on two 7's this winter. Should be fun!:yes:

21FBP22A Mini-Rejuvenation
 

Thanks for your renewed interest in the "21CT55 Test-Bed". Today I turned it on and still got immediate full brightness with perfect focus and boostless CRT heaters at 5.94vac! I agree with Pentode that running the 21FBP22A at 7.64VAC for 2 hours seems to have accomplish a very gentle CRT rejuvenation. It probably cleaned the cathodes and possibly burned-off any control grid contamination. The cut-off glow is virtually gone!


Hey, if all I have to do is occasionally run the Big Sucker at 7-8vac for a couple of hours to restore performance, I think I'll keep it....Tom

Tom, IMO you are asking for another flyback failure running at 30-32KV. That flyback was not designed to run with that much HV. The 21FBP22 has a maximum limit of 27.5KV anode voltage.

He won't listen, I've already told him. Nevermind the fact that if the max ratings are exceeded, x-ray production goes beyond limits deemed acceptable.

Not To Worry, Not to Worry
 

John.....I appreciate your concern for my old 21FBP22A and my new Flyback that's used on at least CT16 thru CT20s. I consider my 21CT55 a bench-top test-bed rather than a candidate for the usual chassis restoration including the mandatory complete recap. My stated long term goal for this test-bed is to demonstrate thru screen-shots the picture quality potential of the wide bandwidth I Q demodulation and low-level matrix processes of the CTC2B chassis teamed with what I consider the best roundy CRT, the grey screen 21FBP22A rare earth. Since I don't consider my 21CT55 a sacred icon of early color TV technology, I am at liberty to take reasonable design risks in the crucial horizontal deflection and EHV ultor system. The original 58 year old FBX that failed developed a short in its primary as the result of rotted insulation due to simple old age rather than over voltage in its secondary.

That said, the replacement FBX's secondary is not the universal winding of the original but a uniform wound solenoid stack of at least 30 to 50 layers! It was completely encapsulated in a multi layered rubbery boot to keep moisture out.

RCA used this FBX in the last 6 or 7 CTCs of the roundy series. I've been using it in my 21CT55 since December 2010 at EHV of 25kv to 35kv with HOT currents of 195ma to 205ma. In all cases it's coil temp has never exceeded 120degF with no fan at room temps of up to 70degF and 112degF at room temps of 95degF with a small fan directed at the FBX. The 21FBP22A is rated at 27.5kv max.This was probably dictated by barely detectable X-ray emissions rather then electrical breakdown within the CRT. It too was subjected to the same sustained 35kv as the FBX secondary. Standard high production engineering practices at RCA would not permit fielding of a consumer product without a proven safety factor of at least 20% to 30%. So 27.5KV times 120% says this FBX CRT combo should run all day with an ultor of 33kv! My performance ultor is now 30kv. The 21CT55 produces this ultor voltage with only 200ma current at the B++ fuze location which is the same current as the HOT cathode current.

Since I feel obligated to push the envelope of the 21CT55 I employ continuous monitoring of all critical parameters during all running of the TV. These include mains input held at 115vac, measure of B++ voltage, HOT current, Boost voltage, Ultor voltage, focus voltage and even CRT heater voltage at the tube socket.

Most importantly, I never allow the TV to run with screen display when I leave the room. I have a switch on the chassis that disconnects the B++ into the horizontal section but leaves all other sections active with tubes on. I hope this drone leaves you and miniman somewhat more comfortable that I'm not unnecessarily destroying a 21CT55 I've had since 1964.

John,


Told ya so. :smoke:

Ah well...concern expressed, now not my problem. :-)

Dosimeter, anyone?

Hello Mr. Tomcomm,

Have you ever done any bench testing / experimenting with broadcast monitors such as Conrac or Sony CVM PVM series? Or are you only interested in the ctc2b/grey screen combination?

I Gots Responces!
 

After three garbled one-liner negative responses to my lengthy rationalization of my CTC2B test-bed effort, one reasonable response was finally posted. Yes, RobtWB I have a Sony PVM-1344Q composite / component pro monitor. I use it as a lab standard when comparing the picture quality of the CTC2B with a perfect comb-filtered pro monitor standard. I will use it after I converge the CTC2B and take screen shots with the new Sony DSR-HX9V camera, soon. Perhaps the three first-responders would care to elaborate on their vehement, specific objections with my present CTC2B operation at 30KV ultor, which is only 9% over max and runs only 200ma HOT current?

I for one already have, in your meltdown thread:

http://videokarma.org/showthread.php...hlight=tomcomm

John Folsom has much more knowledge on these old sets than I ever will, if you won't listen to him why would you listen to me (again)? Let me reiterate that your experiements are worthy, I simply fail to see what you hope to obatin by operating these parts beyond their rated limits. My 21-CT-55 makes a fine picture indeed when operated at normal current and voltages (when the tuner isn't acting up), just ask anyone who's see it. My intuition tells me that you're more likely to find improvements in picture quality by providing a better signal to the CRT, like gutting the decoder entirely and going with something more modern. I don't think anything you're doing with respect to HV production has anything to do with your results, or any improvement in picture quality. Just my opinion.

I will simply add that operating the flyback at elevated voltage levels increases the chances of flyback failure. I have no science to quantify the risk, so if you are happy so be it. I expect there is a very modest radiation risk, you should at least keep the HV cover on (shielding the 6BK4). There is probably some potential risk for a CRT internal arc over, but once again, if you are happy with the risk, so am I. As I said, I just wanted to express my concerns, and after that, it is not my problem to worry about. Have fun!

Hello- I've watched this thread with great enjoyment and also admiration for your skilled work... I have no idea how much of a risk you run with a nominal hv of 30kv but I doubt it's emitting significant x-radiation. It goes without saying that the shields around the rectifier should remain in place at all times. Remember the 70s sets like Zenith that would knock the necks off the tube bell, they were supposedly spiking to about 40kV for that to happen. And of course G-E in the later 60s.
If all seems well, it probably is. Smart to check HO current to make sure.

Nice piece of TV history!:yes:

Much of your video drive experiments I find facinating, and would like to learn more about.

However like Nick and John I would not try to elevate the HV. These sets are plenty bright at 25KV, and any gain from running it high does not sound remotely worth the risk to me.
I reciently revived a CTC4 and on the first run in which I had good video I let it run about an hour, and even though no damage was done, by not preforming the sam's horizontal adjustments, I was kicking my self when after powering down I found the flyback to be warm. If I can't get a fly to run cool and or within factory specs it prevents me from being able to fully enjoy a set as I become paranoid over the possibility that I may be ruining an IMPORTANT piece of a prized possession which I can't readily get a replacement for.

A flyback is like a good car if you treat it gently, and give it the proper care it will out last you, but if you ride it hard and push the limits enough it will eventually fail catistrophicaly.

I guess you are not subjecting it to the worst conditions a fly has endured, but you are still rideing it kinda hard. What you do with it is your business, but if you don't want to be looking for another flyback please make sure to carefully monitor it, and be prepared to pull the plug at the first warning sign of failure.

Good luck! Here is hoping you don't toast another rare fly.

Where Do I Begin Here?
 

Seems I need to reiterate a few items that continue to provoke Member comment.
#1 Why do I insist on running the new FBX and the old CRT at “extreme” ultor voltages? Well RCA and GE 21FBP22 spec sheets specify max operation at 27.5KV. This level is undoubtedly driven by fussy Government X-ray mandate. The specs also notes: “Brilliance and definition decrease with decreasing ultor voltage.” Enough said?
Since brilliance and definition increase is what I’m after why shouldn’t I run at 30Kv (109%max) on a new “modern” FBX that requires only 200ma HOT current, at a winding temp of only 112degF! This new FBX is like a brick compared to the fragile original CTC2B FBX that ran 28KV at 264ma HOT.
#2 miniman has stated that I could ”find improvements in picture quality by providing a better signal to the CRT, like gutting the decoder entirely and going with something more modern”. Apparently he has missed the point of my entire effort to demonstrate the superior picture quality of the original full BW I/Q demodulation and low level matrixing of the CTC2B chassis. Was he serious or just being facetious ?
#3 My CTC2B is not in a cabinet in the living room or bedroom used as a daily watcher. It will always reside in the garage lab and most often not operating when I’m not there. If I’m “experimenting” with it, it will be fully instrumented as I described. Besides I have two spare, exactly the same FBXs in new RCA OEM boxes in a safe place in case of a highly unlikely FBX meltdown.
#4 My grey screen 21FBP22 may not be a 21FBP22 after all. Has any member ever seen a light grey screened FB, most are olive green? Bought mine from a rebuilder for $45 who said it was an FB but it doesn’t have any markings on neck or bulb. Doesn’t all CRT rebuilds have an obvious glass weld on its neck, mine doesn’t? On close screen inspection with mag-glass there are 3dot clusters of identical light grey with single darker grey or black dots between the 3dot clusters. Could my CRT be a replacement 21GUP22 or a 21GVP22? Electronic M posted a full screen color bar off his Silvertone that looked identical to one pic I took off mine, it looked great! He stated someone at ETF said it was a 21GUP22. How about it Tom, does your 21GUP22 have a light grey non-energized screen? Please reply...Tom

Does you tube have a bonded safety glass?

My Unidentified CRT
 

John, not bonded. My CRT had a screen safety glass held in place with a foam rubber ring.

If it is not clear, then it is a grey filter glass, which may explain your phosphor color. I have a 21FBP22 which has had its safety glass removed, and the screen is a slightly greenish tint.

I don't know how to identify you CRT type by looking at the face, but someone else may.

FJP=bonded
FBP=non-bonded

Either one with the safety glass removed will look identical, the tint of the screen will let you know which phosphors are in it. Green=sulphide, paper white=rare earth. That's the way I understand it. The RCA sheet I am reading says the 21FBP22 is an all sulphide tube, but I had a rebuilt one that said right on the side of the box 'rare earth' with a grey screen... So perhaps the FBP's came in both flavors, or it could be that a rare earth tube that was bonded in effect becomes an FBP once the lens is removed.


RE: x-rays

The spec sheet carries a specific warning for shielding, even when operated at it's max ultor voltage of 'only' 27.5kv. Going over that limit implies additional risk of increased production of x-rays, so you're taking your chances. The other very good reason not to push too much voltage is not to protect the chassis, but to protect the tube itself. When the HV is increased, so does risk of internal arc within the tube. If you don't much care about the chassis or tube (or your testicles), I don't suppose it matters. :D Also the 6BK4C shunt regulator sheet rates 'absolute max' plate voltage at 27kv, for the same reasons as the CRT.

RE: brilliance

This is what the spec sheet says:

"Brilliance and definition decrease with decreasing ultor voltage. In general, the ultor voltage should not be less than 20,000 volts."

(the part you left out is in bold, because context matters)

Since the tube is specified to be run between 20-27.5kv, I interpret this to mean that when run at voltages lower than 20kv brightness will decrease. RCA themselves only applied 19.5kv to the early picture tubes with the CTC-5 chassis, so there's some wiggle room on the low end when you are hoping to preserve some level of performance. Where your logic runs amok is assuming that it's all good to use the same wiggle room rule at the upper end, when the reality is that maximum ratings should never be exceeded for safety reasons. I am also a mechanic, I can tell you that the same logic will not fly in engines. "it's good at 10 lbs of boost, there is no problem running 15 lbs through it." I promise you this is not the case, many people have melted expensive parts with that kind of thinking. With high voltage and vintage electronics in close proximity to your body, the chances of walking away from a 'wreck' are not as good as with a car that has air bags. Hope my analogy makes sense, it's about safety more than anything else. I fear for your safety, guess that makes me the 'attack dog' as you put it in your other thread. So be it, at least I said something. I have washed my hands of this.

My goodness. The man has been experimenting with this set for almost fifty years. Experimenting. It hasn't burst into flames so far - do we really need all this bickering back and forth?

It is ironic that somebody would bring the set up only a few hours before it had a major breakdown.....
First off it's screen is not a light gray, but rather a dark gray that matches the mask. It almost looks like a modern dark face CRT with the safety glass on (it has been too long since I have removed the glass to remember the color, and I didn't snap a picture).
http://i1095.photobucket.com/albums/...y/DSCN0433.jpg
It is the (I believe) factory original CRT and is a type 21GUP22.
http://i1095.photobucket.com/albums/...y/DSCN0447.jpg
I believe that this is the color bar pic you mentioned.
http://i1095.photobucket.com/albums/...y/DSCN0432.jpg
I believe that it may have been Mark who said to me at the 2010 ETF meet when I got it that he thought it may be a black matrix type. Which is quite possible. I did some cateracting this summer and was able to compare a genuine black matrix rectangular delta-gun CRT to a regular type of the same size, so if I take the tube out of the Silvertone during trouble shooting (I have to readjust the mountings anyway so why not take it a step farther) I'll get a shot of the phosphor and try to determine if it is a black matrix type.
My set is a clone of an RCA CTC-15 or CTC-16 and lacks the benifit of an IQ demod scheme. I suspect that the alignment is lousy on mine. The colorimetry heretofore has been outstanding (ignoring that the screen adjustment balance tends to vary over the course of warmup and extended viewing), but the picture detail both color and mono can't hold a candle to my 71' Zenith Chromacolor hybrid (when the Zenith's focus and color circuits feel like warming up and doing their jobs that is).

21FBP22 Non Active Screen Color
 

Tom, sorry my innocent inquire broke your Silvertone! I must be more careful in my future posts. Thanks again for your interest in my inquiry and your great screen shot postings. Anyway, I now believe my 21FBP22 can't possibly be a 21GUP22 since I bought it in '64 and its " nonactive screen color" is definitely "paper-white" indicating rare-earth as miniman posted. Its most likely a "rare-earth" 21FBP22A as I always suspected and stated in my posts. So is that good or bad from a Picture Quality standpoint? Are the saturated reds of the rare-earth 21FBP22s more like the 15GP22s and 21AXP22s then the more numerous olive-green screen sulfide 21FBP22s? The last time I saw a 21AXP22 was my Dad's CTC4 when I replaced it with my present 21FBP22A 48 years ago. In fact, I haven't seen another roundy of any kind besides mine ever since. All I know is my 21FBP22A reds are obviously more "RED" then my 13in Sony Pro monitor which has SMPTE-C phosphor and my 27in Sony comb-filtered monitor. Both Sonys are orangeish-red in comparison. I was told the SMPTE-C reds make the reproduction of flesh-tones more natural? I would like to see a rare-earth, paper-white screen 21FBP22 included in any serious comparisons with other 21in roundy including Tom's 21GUP22 and the original 15GP22s.

All rare-earth reds are less orange than the zinc cadmium/sulfide red, especially as the sulfide red shifts even more orange at high beam current. Rare earth reds can vary somewhat among them, but not as orange as the sulfide. The big difference in all tubes after the 21AXP22 is the sulfide green, which is much more yellow than P1; and to some extent the sulfide blue, which is a deeper blue (less cyan) than the 15GP22. Other differences you see in your Sony and other sets can be due to the color matrixing, which was adjusted to get reasonably natural flesh tones. Depending on how much matrix redesign was done, you could also get a sort of auto tint action that reduced the variation in flesh tones to some degree.

You may recall that in some cases when an earlier CRT was replaced with one with more efficient red, there was a change made to the cathode drive to reduce the red Y drive. But the R-Y gain was not reduced. The reason is that the new tube also had a yellower sulfide green. This was like adding some red into every green color, so the high R-Y amplitude tended to compensate by turning off red harder on greenish colors. This corrected the range of hues from red to orange to yellow to green, but also lit up reds too brightly. This compromise was subsequently built into all consumer NTSC sets to some degree, and a SMPTE-agreed amount was built into professional monitors, but with a matrix on/off switch.

Some of the impression of "redder" reds with the older tube comes from the contrast with the P1 green but also is due to the not-overly bright reds (even if they are slightly orange) and/or due to not having a matrix that was fudged to reduce flesh tone variations.

By the way, if you want an example of "how red" NTSC reds should be, note that red traffic signals are outside the NTSC gamut, but incandescent car taillights are not. Most rare-earth tubes are actually close to NTSC red - it's the greens that are way off.

I believe that my setting the Silvertone on the carpet (thus causing the bottom vents to be blocked) because I needed to remove the set it was sitting on to make room for the CTC4 was the reason it quit. I'll have to pull the back to find the scientiffic cause of the failure.

I can't compare the 21GUP side by side to the white face 21FBP until I get the CTC4 (which is using a white face 21FBP) working right, but I can give a qualitative, across-the-Midwest comparison of the 15GP (in the CT-100 at the ETF) and the 21GUP in my set.....The 15GP has deeper greens and better saturated colors overall than any other set I've seen in operation (except maybe Nicks 21-CT-55), but my 21GUP comes closer than any other CRT I own ( and have used in a properly adjusted set) to the stunning colorimetry of the 15GP.